System and method for estimating cell center position for cell ID based positioning

• US 20080096578A1
• Filed: 12/22/2006
• Published: 04/24/2008
• Est. Priority Date: 09/10/2001
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Inventors: Chansarkar, Mangesh, Garin, Lionel, Lin, Xiangdong, Wan, Marlene
• Granted Patent: US 8,165,607 B2
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: G01S 19/06 employing an initial estimate of the location of the receiver as aiding data or in generating aiding data
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/46 the supplementary measurement being of a radio-wave signal type
• CPC Class Codes: G01S 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: H04M 2250/10 including a GPS signal receiver
• CPC Class Codes: H04W 4/02 Services making use of location information

Abstract

Systems and methods for estimating a cell center location in a wireless communication system having an interface to a satellite positioning system (“SPS”) such as for example, a Geosynchronous Positioning System (“GPS”). The wireless communication system provides service to mobile stations within a cell, each mobile station includes a SPS receiver. Examples of the systems and methods for estimating a cell center location analyze the mobile station locations in a cell as a uniform distribution of mobile station locations and calculate a statistical measure characterizing the mobile station locations as a function of the mobile station locations. In one example, the statistical measure is a maximum likelihood mobile station location. In another example, the statistical measure is the mean mobile station location in the cell. The estimated cell center location may be used to approximate the location of the mobile station during a warm or cold restart of the SPS receiver part of the mobile station.

Claims

1. A method for estimating a cell location for a cell that provides wireless communication services to a plurality of mobile stations each mobile station having a Satellite Positioning System (“

SPS”

) receiver operating in a positioning system, the method comprising;

obtaining a mobile station location for each of N mobile stations having a cell identifier that identifies the cell, each mobile station location being determined using the positioning system; and

calculating an estimated location of a cell center based on a statistical measure of the mobile station locations of the N mobile stations in the cell where the statistical measure is either a maximum likelihood location or a mean mobile station location.

2. The method of claim 1 where:

the step of calculating the estimated location of the cell center is based on the maximum likelihood location further comprising;

obtaining an SPS variance, V_j, for each mobile station, j, in the cell;

calculating a cell location variance, V_ij, of a true position of each mobile station j in the cell relative to the estimated cell center location according to;

$V_{\mathrm{ij}}=\left[\begin{array}{cc}{\mathrm{\sigma <br><br>}}_{\mathrm{tj}}^2& 0\\ 0& {\mathrm{\sigma <br><br>}}_{\mathrm{tj}}^2\end{array}\right]+V_j,$

where σ

_tj² is a variance of a true position of the mobile station j relative to a true cell center position;

using the variance V_ij of each mobile station j of N to determine the maximum likelihood mobile station location using;

${\hat{X}}_{\mathrm{ci}}={\left[\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{\mathrm{ij}}^{-1}\right]}^{-1}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{\mathrm{ij}}^{-}<br><br>,$

for the cell i, where N is the number of mobile stations in the cell.

3. The method of claim 2 further comprising the steps of:

determining an initial cell radius, r₀; and

setting σ

_tj²=(r₀/2)².

4. The method of claim 1 where the step of calculating the estimated location of the cell center is based on the mean mobile station location, which further comprises:

for the N mobile stations, calculating the mean using;

$\mathrm{mean}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mobile}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{station}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{location}=\frac{1}{N}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>{\hat{X}}_j<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{where}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\hat{X}}_j<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{is}<br><br>\text{\hspace{1em}<br><br>}<br><br>a<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{vector}$

representation of each mobile station j=1 to N.

5. The method of claim 1 further comprising the steps of:

determining the distances between the estimated cell center location and each of the N mobile stations in the cell;

determining an initial cell radius by determining the distance between the estimated cell center location and the mobile station that is farthest away from the estimated cell center location;

determining a minimized radius r₁ as P % of the initial cell radius;

determining if P % of the N mobile stations in the cell are located within a circle defined by r₁;

if P % of the N mobile stations in the cell are located within a circle defined by r₁, then determine a new estimated cell center location by performing the following steps;

obtaining a mobile station location for each of N mobile stations having a cell identifier that identifies the cell, each mobile station location being determined using the positioning system; and

calculating an estimated location of a cell center based on a statistical measure of the mobile station locations of the N mobile stations in the cell where the statistical measure is either a maximum likelihood location or a mean mobile station location.

6. The method of claim 1 further comprising:

determining the distances between the estimated cell center location and each of the N mobile stations in the cell;

determining an initial cell radius by determining the distance between the estimated cell center location and the mobile station that is farthest away from the estimated cell center location;

determining a distance between the estimated cell center location and the mobile station that is closest to a radius r₁ that defines a circle containing P % of the N mobile stations in the cell;

determining a new estimated cell center location by performing the following steps;

obtaining a mobile station location for each of N mobile stations having a cell identifier that identifies the cell, each mobile station location being determined using the positioning system; and

calculating an estimated location of a cell center based on a statistical measure of the mobile station locations of the N mobile stations in the cell where the statistical measure is either a maximum likelihood location or a mean mobile station location.

7. The method of claim 1 further comprising:

after the step of obtaining the mobile station locations, testing the mobile station locations to determine if the mobile stations are clustered by;

determining an initial cell radius;

defining a plurality of circles having radii less than the initial cell radius with centers at random locations in the cell;

determining if each of the plurality of circles defines an area containing a cluster of uniformly distributed mobile station locations;

for each of the plurality of circles that defines a cluster of uniformly distributed mobile station locations, determining an estimated cluster center location by performing the following steps;

obtaining a mobile station location for each of N mobile stations in the cluster, each mobile station location being determined using the positioning system; and

calculating an estimated location of a cluster center based on a statistical measure of the mobile station locations of the N mobile stations in the cluster where the statistical measure is either a maximum likelihood location or a mean mobile station location.

8. A method for approximating a current mobile station location for a mobile station comprising:

retrieving a cell identifier for the mobile station;

calculating an estimated cell center location by performing the method of claim 1;

and

defining the approximate current mobile station location to be the estimated cell center location.

9. A computer readable medium having a plurality of instructions for performing programmed functions including the method of claim 1.

10. A system for estimating a cell center location in a satellite positioning system (“

SPS”

) comprising;

a SPS server connected to the SPS system to retrieve a plurality of mobile station locations from mobile stations in a cell in a wireless communication system, each mobile station comprising an SPS receiver;

a SPS database for storing the plurality of mobile station locations and a cell identifier to identify the cell in which the mobile station is obtaining wireless communications service; and

a cell center location estimator for calculating an estimated cell center location by obtaining N mobile station locations assumed to be uniformly distributed in a cell i and calculating a statistical measure of the mobile station locations, where the statistical measure is either a maximum likelihood mobile station location or a mean mobile station location.

11. The system of claim 10 where the SPS database stores a horizontal variance, V_j of each mobile station location as determined by the SPS positioning system;

and the cell center location estimator further comprises;

a variance calculation function for calculating a variance of a true position of each of the N mobile stations relative to an estimated cell center as a function of V_j; and

a maximum likelihood mobile station location function for calculating the maximum likelihood mobile station location as a function of the variance of the true position of each of the N mobile stations relative to the estimated cell center location and the N mobile station locations.

12. The system of claim 11 where:

the variance calculation function calculates the variance of the true position of each of the N mobile stations relative to the estimated cell center location using;

$V_{\mathrm{ij}}=\left[\begin{array}{cc}{\mathrm{\sigma <br><br>}}_{\mathrm{tj}}^2& 0\\ 0& {\mathrm{\sigma <br><br>}}_{\mathrm{tj}}^2\end{array}\right]+V_j,$

where σ

_tj² is a variance of a true position of the mobile station j relative to a true cell center position, and where σ

_tj²=(r₀/2)² where r₀ is the initial cell radius; and

the maximum likelihood mobile station location function calculates the maximum likelihood mobile station location using;

${\hat{X}}_{\mathrm{ci}}={\left[\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{\mathrm{ij}}^{-1}\right]}^{-1}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>V_{\mathrm{ij}}^{-}<br><br>,$

for the cell i, where N is the number of mobile stations in the cell.

13. The system of claim 10 where the cell center location estimator further comprises a mean mobile station location function to calculate the mean mobile station location of the N mobile stations.

14. The system of claim 13 where the mean mobile station location function calculates the mean mobile station location using:

15. The system of claim 10 where the cell center location estimator further comprises a mobile station location filter to find a minimum radius defining a circle around a first estimated cell center location that includes a selected percentage of the N mobile station locations where the selected percentage of the N mobile station locations location.

16. The system of claim 10 where the cell center location estimator further comprises a mobile station location filter to select a selected percentage of the N mobile station location that are closest to a first estimated cell center location where the selected percentage of N mobile stations is used by the cell center location estimator to calculate a second estimated cell center location.

17. The system of claim 10 further comprising:

a cluster center location estimator for defining a plurality of clusters of mobile stations in the cell, each cluster containing a number N_c of mobile stations where the cell center location estimator is used to determine the cluster center location for N=N_c.

18. A computer readable medium having programmed instructions for operation in a wireless communication system that uses a satellite positioning system (“

SPS”

), the computer readable medium comprising;

a SPS database interface for retrieving data relating to a plurality of mobile stations in a cell of the wireless communications system, the data including, for each mobile station, a mobile station location and a cell identifier to identify the cell in which the mobile station is obtaining wireless communications service; and

a plurality of programmed instruction for calculating an estimated cell center location by obtaining N mobile station locations assumed to be uniformly distributed in a cell i and calculating a statistical measure of the mobile station locations, where the statistical measure is either a maximum likelihood mobile station location or a mean mobile station location.

19. A computer readable medium according to claim 18 where the SPS database stores a horizontal variance, V_j of each mobile station location as determined by the SPS positioning system;

and the computer readable medium further comprises;

a second plurality of programmed instructions for calculating a variance of a true position of each of the N mobile stations relative to an estimated cell center as a function of V_j; and

a third plurality of programmed instructions for calculating the maximum likelihood mobile station location as a function of the variance of the true position of each of the N mobile stations relative to the estimated cell center location and the N mobile station locations.

20. A computer readable medium according to claim 18 further comprising a fourth plurality of programmed instructions to calculate the mean mobile station location of the N mobile stations.

21. A computer readable medium according to claim 18 further comprising a fifth plurality of programmed instructions to find a minimum radius defining a circle around a first estimated cell center location that includes a selected percentage of the N mobile station locations where the selected percentage of the N mobile station locations location.

22. A computer readable medium according to claim 18 further comprising a sixth plurality of programmed instructions to select a selected percentage of the N mobile station location that are closest to a first estimated cell center location where the selected percentage of N mobile stations is used by the cell center location estimator to calculate a second estimated cell center location.

23. A computer readable medium according to claim 18 further comprising:

a seventh plurality of programmed instructions for defining a plurality of clusters of mobile stations in the cell, each cluster containing a number N_c of mobile stations where the plurality of programmed instruction for calculating an estimated cell center location is used to determine the cluster center location for N=N_c.

24. An apparatus in a wireless communication system a satellite positioning system (“

SPS”

) comprising;

a first interface to a SPS database for retrieving from storage in the SPS database a plurality of mobile station locations corresponding to a plurality of mobile stations operating in a cell of the wireless communication system and a cell identifier to identify the cell in which the mobile station is obtaining wireless communications service; and

a cell center location estimator for calculating an estimated cell center location by obtaining N mobile station locations assumed to be uniformly distributed in a cell i and calculating a statistical measure of the mobile station locations, where the statistical measure is either a maximum likelihood mobile station location or a mean mobile station location.

25. The apparatus of claim 24 where the first interface to the SPS database retrieves a horizontal variance, V_j of each mobile station location as determined by the SPS positioning system;

and the cell center location estimator further comprises;

a variance calculation function for calculating a variance of a true position of each of the N mobile stations relative to an estimated cell center as a function of V_j; and

a maximum likelihood mobile station location function for calculating the maximum likelihood mobile station location as a function of the variance of the true position of each of the N mobile stations relative to the estimated cell center location and the N mobile station locations.

26. The apparatus of claim 24 where the cell center location estimator further comprises a mean mobile station location function to calculate the mean mobile station location of the N mobile stations.

27. The apparatus of claim 24 where the cell center location estimator further comprises a mobile station location filter to find a minimum radius defining a circle around a first estimated cell center location that includes a selected percentage of the N mobile station locations where the selected percentage of the N mobile station locations location.

28. The apparatus of claim 24 where the cell center location estimator further comprises a mobile station location filter to select a selected percentage of the N mobile station location that are closest to a first estimated cell center location where the selected percentage of N mobile stations is used by the cell center location estimator to calculate a second estimated cell center location.

29. The apparatus of claim 24 further comprising:

a cluster center estimator for defining a plurality of clusters of mobile stations in the cell, each cluster containing a number N_c of mobile stations where the cell center location estimator is used to determine the cluster center location for N=N_c.